《經濟學專業英語教程（精編版）》

Text:DemandandSupply（需求與供給）

1.Keywords2.Howarepricesdetermined?3.Demandschedulesandcurves4.Supplyschedulesandcurves5.Changesindemand6.Changesinsupply7.Questions1.KeywordsfreeenterprisepricemechanismmakeaprofiteffectivedemandlawofdemandlawofsupplydemandscheduledemandcurveverticalaxishorizontalaxissupplyschedulesupplycurvemarketmechanismequilibriumpricerelatedgoodsconsumertastesFutureexpectationschangesindemandchangesinsupply2.Howarepricesdetermined?2.1Pricemechanism2.2Demandandeffectivedemand2.3Lawofdemandandlawofsupply2.1PricemechanismIfaneconomyrunsonthelinesofthepurelycompetitivemarketoffreeenterprise,thenwhatisproducedandthepricesatwhichtheproductsaresolddependuponthechoicesanddecisionsmadebyconsumersandproducers.Thepricemechanismistheprocessbywhichpricesriseandfallasaresultofchangesindemandandsupply,andtherebyactsasasignaltoproducerstoguidethemontheirproductionplans.Ifoureconomywereentirelycompetitiveandtherewerenorestrictionsatall,thenthemarketforces,orpricemechanism,wouldoperatefreely.Theonlythingsthatwouldbeproducedwouldbethosegoodsforwhichconsumerswerewillingtopaysufficienttomakeitworthwhilefortheproducerstoputthemonthemarket.Thedemandforaproductandthepriceatwhichitcanbesoldindicatetotheproducerthebestwaytoallocateresourcesinordertomakeaprofit.2.2DemandandeffectivedemandDemandmeansthequantitywhichbuyersarewillingtopurchaseatagivenpriceoveragivenperiodoftime.Effectivedemandmeansadesiretoobtainanarticleaccompaniedbytheabilityandwillingnesstopayforitatthepriceasked.Ineconomics,whenwespeakofdemand,weareusuallyreferringtoeffectivedemand.2.3LawofdemandandlawofsupplyLawofdemandBuyersarelikelytobuymoreofanitemasthepricefalls.LawofsupplyAspricesrise,sellerswouldliketosellmoreandwill,ifitispossible,offeralargerquantityforsale.3.Demandschedulesandcurves3.1Demandschedules3.2Demandcurves3.1DemandschedulesPrice(cents/kg)Quantitydemanded(kg)Price(cents/kg)Quantitydemanded(kg)107050302060602030507010404080Nil3.2DemandcurvesThepriceisshownontheverticalaxis,whilequantityisshownonthehorizontalaxis.Thisistheconventionalwayofdrawingademandandsupplygraph.Aspricesfall,alargerquantityofagoodisdemanded.Thetypicaldemandcurveslopesdownfromlefttoright.Thisindicatesthatconsumersbuymoreofagoodatlowerpricesandlessathigherprices,butatverylowpricesdemanddoesnotnecessarilyincrease.Thisissometimescalledanexpansionorcontraction,oramovementalongthecurve.4.Supplyschedulesandcurves4.1Supplyschedules4.2Supplycurves4.3Equilibriumprice4.1SupplyschedulesPrice(cents/kg)Quantitysupplied(kg)Price(cents/kg)Quantitysupplied(kg)8010040607090305060802040507010304.2SupplycurvesAspricesrise,alargerquantityofagoodissuppliedorsold.Thetypicalsupplycurveslopesdownfromrighttoleft.Thisindicatesthatsuppliersorsellerssupplyorsellmoreofagoodathigherpricesandlessatlowerprices.Thisiscalledamovementalongthecurve.4.3EquilibriumpriceAcompromisebetweenhowmuchandatwhatpricethesellerdecidestosellandtheconsumers’planstobuymustbearrivedat.Thisiscalledtheequilibriumpriceandisthepriceatwhichthebuyerispreparedtobuythequantitywhichthesellerispreparedtosellatthatprice,sothatthemarketisclearedandthereisnosurplusandnoshortage.5.Changesindemand5.1Influenceswhichcanchangedemandforgoodsandservices5.2Changesindemand5.1InfluenceswhichcanchangedemandforgoodsandservicesPricereceivedfortheitemPricesofrelatedgoodsChangesinconsumertastesPricesofallothergoodsandservicesTheincomeoftheconsumerFutureexpectations5.2ChangesindemandDemandchangessimplybecausepriceischanging,butnoneoftheotherfactorswhichaffecttheconsumersbuyinghavechanged.Achangeinthepriceofagoodresultsinamovementalonganexistingdemandcurve.Pricehasremainedunchangedbuttherehasbeenachangeindemandcausedbyfactorsotherthanprice.Thedemandcurvecouldshifttotheleftorrightifthereisachangeinanyoftheseconditionsotherthanprice,influencingpeopletobuylessormoreofacommodityevenifthepriceremainsunchanged.6.Changesinsupply6.1Influenceswhichcanchangesupplyforgoodsandservices6.2Changesinsupply6.1InfluenceswhichcanchangesupplyforgoodsandservicesThepricereceivedfortheitemThecostofproducingtheitemTaxesimposedwhichraisetheitem’smarketpricetoconsumersSubsidiesawardedtoproducers,whichreducethecostsofproductionPricesofothergoodsFutureexpectationsChangesinsupplyduetothenatureofthegood6.2ChangesinsupplyInthecaseofsupply,anychangeofpriceresultsinamovementupordowntheexistingsupplycurve,ifnootherchangesoccurtoaffectsupply.Anychangeintheconditionsotherthanmarketpricescausesashiftinthesupp